Automatic injection devices have previously been disclosed in the patent literature. Automatic injection devices contain some sort of power reservoir where electrical or mechanical energy can be accumulated. The accumulated energy is easily released by actuating a release mechanism whereby the accumulated energy assists the user in injecting a set dose of medicine and/or assisting needle insertion.
For example, EP 0 516 473 A1 discloses an injection device having a needle which, when the device is operated, is first caused to project, then liquid is forced out through it, and finally the needle is automatically retracted. The needle extends forwardly from a capsule that can slide longitudinally within a barrel-like body, a relatively weak spring normally maintaining the capsule and needle retracted. A more powerful spring acts oppositely on a plunger which, when released, shoots the capsule forward by acting on the liquid therein, and then forces the liquid out through the projecting needle. At the end of the forward stroke the plunger and capsule are decoupled and the weak spring returns the exhausted capsule and its needle to the retracted position. The spring acting on the plunger can be released by a release button positioned on the outer surface of the injection device.
In WO 01/41838 discloses a handheld injection device by which set doses of a liquid medicament can be injected from a medical reservoir, such as cylinder ampoule, by release of a power reservoir in the device. The power reservoir can either be an electric battery by which a motor can be energized to press out a set dose of medicine, or a strained spring maintained in its strained position by a detent which spring when released can press out a set dose of medicine. When the power reservoir is released, the liquid medicine will be pressed out from the cylinder ampoule through an injection needle mounted on the cylinder ampoule or on the injection device carrying the cylinder ampoule. The power reservoir is released fully or partially by activating a release button, such as an electric switch, located on the housing of the injection device and in the distal half of the length of the injection device. By making at least a part of the distal third of the injection device of an ergonomic shaped cross section, the user can grip the injection device as a pencil is gripped by a thumb, an index finger and a long finger.
In both EP 0 516 473 A1 and WO 01/41838 the release buttons are positioned on an outer surface of the injection devices. In EP 0 516 473 A1 the release button is position on the outer side of the cylindrical body, whereas in WO 01/41838 the release button is positioned close to the injection needle of the injection device. However, it may be advantageous to position the release button or mechanism so that the injection device can be activated by providing a force to the upper region of the injection device—preferably to a release button or mechanism arranged axially with the injection device.
It is an object of the present invention to provide an automatic and handheld mechanical injection device having a combined release member and dose setting member.
It is a further object of the present invention to provide an automatic and handheld mechanical injection device where an injection of a set dose can be initiated using the thumb or the index finger of the hand handling the injection device by providing an axial force to an upper region of the injection device.
It is a still further object of the present invention to provide an automatic and handheld mechanical injection device having an exterior design very similar to conventional manual injection devices.